In a semiconductor device manufacturing process, various heat treatments such as film formation, etching, oxidation/diffusion, modification, annealing and the like are performed on a semiconductor wafer as a substrate to be processed. Such heat treatments are generally performed by heating the semiconductor wafer by using a substrate processing apparatus having a heating lamp or a heater.
However, recently, an apparatus using a microwave instead of a lamp or a heater is known as the apparatus for performing heat treatment on the semiconductor wafer. For example, Japanese Patent Application Publication No. 2009-516375 (JP2009-516375A) describes a heat treatment system for performing hardening, annealing and film formation by using a microwave energy. Further, Japanese Patent Application Publication No. 2010-129790 (JP2010-129790A) describes a heat treatment apparatus for forming a thin film by heating a film forming material by irradiating a microwave to a semiconductor wafer having a film forming material layer formed on a surface thereof. Especially, in the microwave processing apparatus, it is possible to form a thin active layer while suppressing diffusion of impurities or restore a lattice defect.
Japanese Patent Application Publication No. 2005-259633 (JP2005-259633A) describes a microwave plasma discharge processing apparatus having a plurality of magnetron high-frequency oscillators although it is different from the microwave processing apparatus described in JP2009-516375A and JP2010-129790A. Further, JP2005-259633A describes a technique for performing impedance matching in a high-density plasma region between the magnetron high-frequency oscillator and a low-density plasma region where a processing specimen is provided in the microwave plasma discharging processing apparatus.
In the microwave processing apparatus, a magnetron is generally used as a microwave source for generating a microwave. When an output of a single magnetron is insufficient for a large semiconductor wafer having a diameter of about 300 mm or the like, a plurality of magnetrons is provided to introduce a plurality of microwaves into the processing chamber simultaneously.
Meanwhile, in the microwave processing apparatus, e.g., a surface state or a temperature of the semiconductor wafer is changed as the semiconductor wafer is processed, so that an impedance of the processing chamber side is changed. Accordingly, it is preferable to perform impedance matching between the microwave source and the processing chamber even while the semiconductor wafer is being processed. The impedance matching is performed when a power of a reflection wave transmitted from the processing chamber side to the microwave source exceeds a predetermined threshold value, for example.
When a plurality of microwaves is introduced into the processing chamber simultaneously as described above, a microwave generated by another microwave source is introduced between the microwave source and the processing chamber and, thus, it is difficult to detect the reflection wave accurately. In that case, the accuracy of the impedance matching may be inhibited.
JP2009-516375A and JP2010-129790A do not describe a specific method for matching impedance. JP2005-259633A describes a technique for matching impedance in a plasma processing apparatus as described above, but does not describe a method for matching impedance in a microwave processing apparatus other than the plasma processing apparatus.